US8702876B2 - Steel plate having a low welding crack susceptibility and a yield strength of 800MPa and manufacture method thereof - Google Patents

Steel plate having a low welding crack susceptibility and a yield strength of 800MPa and manufacture method thereof Download PDF

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US8702876B2
US8702876B2 US12/524,311 US52431108A US8702876B2 US 8702876 B2 US8702876 B2 US 8702876B2 US 52431108 A US52431108 A US 52431108A US 8702876 B2 US8702876 B2 US 8702876B2
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steel plate
steel
crack susceptibility
welding crack
rolling
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Liandeng Yao
Xiaoting Zhao
Sixin Zhao
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Boashan Iron & Steel Co Ltd
Baoshan Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
    • B21B1/26—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process by hot-rolling, e.g. Steckel hot mill
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations

Definitions

  • the present invention relates to a high strength structural steel, in particular, to a superfine bainite ferrite plate having a low welding crack susceptibility and a yield strength of 800 MPa.
  • Cold welding crack is a very common defect in welding process.
  • the high strength steel of low or middle alloy is welded, as the strength level increases, the propensity to form cold crack becomes greater.
  • preheating before welding and heat treatment after welding is usually required, thus, the greater the strength is, the higher the preheating temperature is, which leads to the complexity of the welding process and un-operability in some special cases, and endangers the safe reliability of welding structures, especially for large steel structures.
  • the welding crack susceptibility index Pcm of steel is required to be as low as possible. Accordingly, a high strength steel plate having a low welding crack susceptibility has been developed in the metallurgy field.
  • a high strength steel having a low welding crack susceptibility also called as CF steel, is a type of low-alloy high-strength steel of excellent welding property and low-temperature toughness, whose advantages are that preheating is not required before welding or a little preheating is required without the generation of crack, which mainly solves the welding procedure problem of large steel structures.
  • thermo-mechanical controlled rolling and cooling processes can overcome this defect.
  • the thermo-mechanical controlled rolling and cooling processes can refine the crystal grains, thus improving the low-temperature toughness of the steel.
  • the alloying components of the steel having a low welding crack susceptibility produce by TMCP technology are typically Mn—Ni—Nb—Mo—Ti and Si—Mn—Cr—Mo—Ni—Cu—Nb—Ti—Al—B systems.
  • the chemical components of a low-alloy, high-strength steel produced by TMCP process disclosed in international publication WO99/05335 are as follows: (wt. %: percent by weight): C: 0.05-0.10 wt. %, Mn: 1.7-2.1 wt. %, Ni: 0.2-1.0 wt. %, Mo: 0.25-0.6 wt. %, Nb: 0.01-0.10 wt.
  • wt. % percent by weight
  • C 0.01-0.05 wt. %
  • Si 0.05-0.5 wt. %
  • Mn 1.0-2.2 wt. %
  • Ni 0.0-1.0 wt. %
  • Mo 0.0-0.5 wt. %
  • Cr 0.0-0.7 wt. %
  • Cu 0.0-1.8 wt. %
  • Nb 0.015-0.070 wt. %
  • B 0.0005-0.005 wt. %
  • Al 0.015-0.07 wt. %.
  • the alloying elements of the above two disclosed steels are designed as Mn—Ni—Nb—Mo—Ti and Si—Mn—Cr—Mo—Ni—Cu—Nb—Ti—Al—B systems, respectively. Since Mo and Ni are both noble metals, the production costs of these types of steel plates are relatively high from the point view of the type and the total addition amount of the added alloying elements. In addition, they both use tempering heat treatment, which increases the manufacture procedures of the steel plate and enhances the production cost of the steel plate, and their Pcm values are relatively high, which has an adverse impact on welding performance.
  • the present inventors use the steel of a Si—Mn—Nb—Mo—V—Ti—Al—B system, and the present inventors design a superfine bainite battened steel plate having a low welding crack susceptibility and a yield strength of 800 MPa by use of the reinforcement effect of V, and thermo-mechanical controlled rolling and cooling processes without thermal refining, the resultant steel plate having excellent low-temperature toughness and weldability.
  • the object of the present invention is to provide a steel plate having a low welding crack susceptibility and a yield strength of 800 MPa.
  • the other object of the present invention is to provide a manufacture method for the steel plate having a low welding crack susceptibility.
  • a steel plate having a low welding crack susceptibility and a yield strength of 800 MPa which comprises the following chemical components (wt. %: percent by weight): C: 0.03-0.08 wt. %, Si: 0.05-0.70 wt. %, Mn: 1.30-2.20 wt. %, Mo: 0.10-0.30 wt. %, Nb: 0.03-0.10 wt. %, V: 0.03-0.45 wt. %, Ti: 0.002-0.040 wt. %, Al: 0.02-0.04 wt. %, B: 0.0010-0.0020 wt. %, the balance being Fe and unavoidable impurities, and the welding crack susceptibility index meets the following formula: Pcm ⁇ 0.20%.
  • the steel plate with a low welding crack susceptibility has a superfine bainite battened structure.
  • the welding crack susceptibility index Pcm is an index reflecting the welding cold crack prospensity of steel.
  • Good weldability refers to a steel which uneasily generates welding crack upon welding, while poor weldability refers to a steel which easily generates crack.
  • preheating of the steel is required before welding, and the better the weldability is, the lower the required preheating temperature is, contrarily, the higher preheating temperature is required.
  • Pcm value for the steel of trademark Q800CF should be lower than 0.28%.
  • the Pcm of the steel plate with a low welding crack susceptibility of the present invention is lower than 0.20%, which accords with the stipulations of the above standard and has an excellent welding property.
  • C Enlarging an austenitic area.
  • C in a supersaturated ferrite structure formed in the quenching process can increase the intensity of the steel.
  • C has an adverse impact on welding performance. The higher the content of C is, the poorer the welding performance is.
  • a bainitic steel produced by TMCP process the lower the content of C is, the better the toughness is, and a lower C content can produce a thicker steel plate of higher toughness, and a superfine bainitic matrix structure containing a high dislocation density can be obtained. Therefore, the content of C in the present invention is controlled at 0.03 to 0.08 wt %.
  • Si Not forming carbide in the steel, but existing in the bainite, ferrite or austenite in the form of a solid solution, which can improve the intensity of the bainite, ferrite or austenite in the steel, and the solution strengthening effect of Si is stronger than that of Mn, Nb, Cr, W, Mo and V. Si can also reduce the diffusion velocity of carbon in the austenite, and makes the ferrite and pearlite C curve in the CCT curve move rightwards, thus facilitating the forming of bainite structure in the continuous cooling process. In the inventive steel, no more than 0.70 wt % of Si is added, which is favourable to improve the matching relation of intensity and toughness of the steel.
  • Mo A ferritizing element, which reduces the austenitic area. Mo, solid solved in austenite and ferrite, can increase the intensity of the steel, improve the hardenability of the steel and prevent temper brittleness. Since the present invention does not need the treatment of thermal refining, only no more than 0.30 wt % of Mo, which is a very expensive element, is added to achieve the purpose of reducing the cost.
  • Nb In the present invention, a relatively high amount of Nb is added in order to realize two purposes, in which one purpose is to refine crystal grains and increase the thickness of the steel plate, and the other purpose is to enhance the non-recrystallization temperature of the steel and facilitates the use of relatively high finish rolling temperature in the rolling process, thus accelerating the rolling speed and increasing the production efficiency. In addition, since Nb strengthens the grain refining effect, thicker steel plate can be produced. In the present invention, 0.03-0.10 wt. % of Nb is added to give consideration to the solution strengthening effect and the fine grain strengthening effect of Nb.
  • V A ferritic formation element, which reduces austenitic area significantly.
  • V dissolved in an austenite at a high temperature can improve the hardenability of the steel.
  • the carbide of V, i.e. V 4 C 3 in the steel is relatively stable, and can inhibit the movement of the grain boundary and the growth of the crystal grains.
  • V can refine the as cast structure of welding metal, reduce the overheating sensitivity of the heat affected zone, and prevent the excessive growth and coarsening of the grains near the fusion line in the heat affected zone, which is favorable to the welding performance.
  • 0.03-0.45 wt. % of V is added to improve the intensity of the steel greatly.
  • V and Cu can both play a role of precipitation strengthening in the steel, however, in comparison with Cu, only a minute quantity of V is added to achieve the same precipitation strengthening effect.
  • V tends to induce the grain boundary cracks in the steel
  • Ni which also a very expensive alloy element, the adding amount of which is at least half of the amount of Cu, must be added to avoid the cracks. Therefore, replacing Cu with V can greatly reduce the manufacturing cost of the steel.
  • Ti A ferritic formation element, which reduces austenitic area significantly.
  • the carbide of Ti i.e. TiC
  • Ti is relatively stable, and can inhibit the growth of the crystal grain.
  • Ti solid solved in austenite, is favourable to improve the hardenability of the steel.
  • Ti can reduce the first type of the temper brittleness, i.e. 250-400° C. temper brittleness. Since the present invention does not need the thermal refining, the adding amount of Ti can be reduced. In the present invention, 0.002-0.040 wt. % of Ti is added, which forms fine carbonitride to precipitate out, thus refining the Bainite battened structure.
  • Al can increase the driving force of the phase change from austenite to ferrite and can intensively reduce the phase cycle of the austenite.
  • Al interacts with N in the steel to form fine and diffusive AlN, which precipitates out and can inhibit the growth of the crystal grain, thus achieving the purpose of refining crystal grains and improving the low temperature toughness of the steel. Too high content of Al will have an adverse impact on the hardenability and welding performance of the steel.
  • no more than 0.04 wt. % of Al is added to refine crystal grains, improve the toughness of the steel and guarantees the welding performance.
  • B can dramatically increase the hardenability of the steel.
  • 0.001-0.002wt. % of B is added so that one can readily obtain a high intensity bainite structure from steel under a certain cooling conditions.
  • a manufacturing method of a steel plate having a low welding crack susceptibility and a yield strength of 800 MPa which comprises smelting, casting, heating, rolling and cooling procedures, wherein after rolling procedure, the steel is subjected to the cooling procedure without the thermal refining.
  • the thickness of the casted continuous casting billet or steel ingot is not less than 4 times of the thickness of the finished steel plate.
  • the heating temperature in the heating process is 1050 to 1180° C.
  • the holding time is 120 to 180 minutes.
  • the rolling is divided into the first stage of rolling and the second stage of rolling.
  • the start rolling temperature is 1050 to 1150° C., and when the thickness of the rolled piece reaches twice to three times of that of the finished steel plate, the rolled piece stays on the roller bed until the temperature reaches 800-860° C.
  • the Pass deformation rate in the second stage of rolling is 10-28%, and the finish rolling temperature is 780-840° C.
  • the steel plate in the cooling process, enters an accelerated cooling device and is cooled at a rate of 15 to 30° C./S to a temperature of 350 to 400° C., followed by air cooling.
  • the air cooling is performed by the way of cooling in packed formation or bank cooling.
  • the non-recrystallizing temperature is about 950 to 1050° C., and it is firstly rolled at a relatively high temperature from 1050 to 1150° C. to produce a certain dislocation density in the austenite, then during the relaxation process of lowering the temperature to roll the billet to 800-860° C., the inside of the austenite crystal grains is subjected to a restoration and statically recrystallization process, thus refining the austenite crystal grains. In the relaxation process, individual precipitation and complex precipitation of carbonitride of Nb, V and Ti occur.
  • the precipitated carbonitride pins the dislocation and subgrain boundary movement, reserves a lot of dislocation in the austenite crystal grains, and provides a lot of nucleation sites for the formation of bainite during the cooling process. Rolling at 800-860° C. greatly increases the dislocation density in the austenite, and the carbonitride precipitated at the dislocation inhibits the coursing of the deformed crystal grains. Due to the precipitating effect caused by deformation, a relatively large Pass deformation will facilitate the formation of finer and more diffusive educts.
  • High dislocation density and fine and diffusive educts provide high density of nucleation sites for bainite, and the pining effect of the second phase particles to the bainite growth interface inhibits the growth and coursing of the bainite battern, which is beneficial for both the intensity and toughness of the steel.
  • the finish rolling temperature is controlled in the low temperature section of the non-recrystallization zone, and at the same time, this temperature section is close to the transmission point Ar 3 , i.e. the finish rolling temperature is 780-840° C., and finishing rolling within this temperature range can increase the defects in the austenite by increasing the deformation and inhibiting the restoration, thus providing higher energy accumulation for the bainite phase change while not bringing about too much burden to the roller, suitable for producing thick plate.
  • ⁇ G chem should be considered in combination with the strain stored energy ⁇ G d caused in the rolling process to increase the driving force of the bainite nucleation. Due to the high dislocation density in the crystal grains, the nucleation sites of bainite increase. Considered by combining the thermodynamic and dynamic factors, the bainite can nucleate at a very large speed. Rapid cooling speed enables the bainite transformation to be completed quickly and inhibits the coarsing of the bainite ferrite battern. After exiting from the accelerated cooling device, the steel is cooled in packed formation at 450-550° C. or air cooled in a cold bed to make the carbide of V in the ferrite precipitate more completely, thus enhancing the contribution of the precipitation strengthening to the intensity.
  • the steel for high intensity mechanical equipment and engineering construction needs high intensity and excellent toughness.
  • Thermo-mechanical treatment of the steel plate is usually done by Thermo-mechanical Controlled Rolling and Controlled Cooling Process (TMCP), which refines the microstructures or forms the high intensity structures such as ultra-fine bainite by controlling-deformation rate and cooling rate, thus improving the yield strength of the steel.
  • TMCP Thermo-mechanical Controlled Rolling and Controlled Cooling Process
  • Modified TMCP and Relaxation Precipitation Controlling (RPC) technology form a stable dislocation network, diffusive and fine second phase particles precipitate out at the dislocation and subgrain boundary, the bainite battern is refined by promoting the nucleation and inhibiting its growth, and a combined action of dislocation strengthening, precipitation strengthening and fine grain strengthening is produced, thus improving the intensity and roughness of the steel.
  • RPC Relaxation Precipitation Controlling
  • the steel plate fully deforms in the recrystallization zone and the deformed austenite produces a high defect accumulation, thus greatly increasing the dislocation density in the austenite.
  • Restoration and recrystallization occurring during the rolling refine the original austenite crystal grains.
  • dislocation within the crystals will re-arrange during the controlled cooling relaxation. Since a hydrostatic pressure field exits in the edge dislocation, interstitial atom such as B will enrich to the dislocation, grain boundary and subgrain boundary, reduce the dislocation mobility, and finally the high density dislocation caused by the deformation will evolve during the restoration to form a stable dislocation network.
  • the microalloy elements such as Nb, V, Ti and the like precipitate out at the grain boundary, subgrain boundary and dislocations in the form of carbonitride of different stoichiometric ratios such as (Nb,V,Ti) x (C,N) y and the like.
  • the second phase particles such as the precipitated carbonitrides, pin the dislocations and subgrain boundary within the crystal grains and stabilize the substructures such as dislocation wall.
  • the dislocation density of austenite is increased by the second stage of rolling process.
  • the effects of the austenite with dislocation and precipitation formed by relaxation process on the following phase transformation can be interpreted as (different from the circumstance that after deformation, no relaxation occurs and a lot of dislocations disorderly distribute): firstly, a subgrain boundary which has a certain orientation difference is a preferred position for the nucleation, and if a second phase, which has an incoherent interface with the matrix, precipitates out, it will facilitate the new phase nucleation, and, after relaxation, a lot of new phase crystal grain will nucleate within the original austenite crystal grains.
  • TMCP plus RPC process forms a high density of dislocation network structure, and the second phase precipitation material points provide a lot of potential nucleation sites for the nucleation of the bainite ferrite, and, the daggling effect of the second phase particles to the moving interface and the evolved subgrain boundary inhibits the growth of the bainite.
  • the manufacturing process of the present invention can play a combined role of promoting the nucleation of the bainite and inhibiting the growth of the bainite, thus refining the final structure.
  • FIG. 1 a is a scanning electron microscope (SEM) micrograph showing the microstructure of the steel plate having a low welding crack susceptibility of the present Example 5.
  • FIG. 1 b is a transmission electron microscope (TEM) micrograph showing the microstructure of the steel plate having a low welding crack susceptibility of the present Example 5.
  • TEM transmission electron microscope
  • the chemical components as shown in Table 1 were smelt in an electric furnace or a converter and casted to a continuous casting billet or steel ingot, which was then heated to 1100° C. for 120 min and was subjected to the first stage of rolling in a middle, thick rolling mill, wherein the start rolling temperature in the first stage of rolling was 1050° C.; and, when the thickness of the rolled piece was 60 mm, it stayed in the roller bed until the temperature reached 850° C., and then the second stage of rolling was performed, wherein the Pass deformation rate in the second stage of rolling was 15-28%, the finish rolling temperature was 830° C., and the thickness of the finished steel plate was 20 mm. After the rolling was complete, the steel plate was delivered into an accelerated cooling (ACC) device, and cooled to 500° C. at a cooling rate of 30° C./s, followed by cooling in packed formation or in a cold bed.
  • ACC accelerated cooling
  • Example 1 It was performed as Example 1 with the exception that the heating was performed at 1050° C. for 240 min, wherein the start rolling temperature in the first stage of rolling was 1040° C., and the thickness of the rolled piece was 90 mm; the start rolling temperature in the second stage of rolling was 840° C., the Pass deformation rate was 15-20%, the finish rolling temperature was 810° C., and the thickness of the finished steel plate was 30 mm; and, the cooling rate of the steel plate was 25° C./S, and the final temperature was 490° C.
  • Example 1 It was performed as Example 1 with the exception that the heating was performed at 1150° C. for 150 mins, wherein the start rolling temperature in the first stage of rolling was 1080° C., and the thickness of the rolled piece was 120 mm; the start rolling temperature in the second stage of rolling was 830° C., the Pass deformation rate was 10-15%, the finish rolling temperature was 820° C., and the thickness of the finished steel plate was 40 mm; and, the cooling rate of the steel plate was 20° C./S, and the final temperature was 530° C.
  • Example 1 It was performed as Example 1 with the exception that the heating was performed at 1120° C. for 180 min, wherein the start rolling temperature in the first stage of rolling was 1070° C., and the thickness of the rolled piece was 150 mm; the start rolling temperature in the second stage of rolling was 830° C., the Pass deformation rate was 10-20%, the finish rolling temperature was 800° C., and the thickness of the finished steel plate was 50 mm; and, the cooling rate of the steel plate was 15° C./S, and the final temperature was 515° C.
  • Example 1 It was performed as Example 1 with the exception that the heating was performed at 1130° C. for 180 min, wherein the start rolling temperature in the first stage of rolling was 1080° C., and the thickness of the rolled piece was 150 mm; the start rolling temperature in the second stage of rolling was 840° C., the Pass deformation rate was 10-15%, the finish rolling temperature was 810° C., and the thickness of the finished steel plate was 60 mm; and, the cooling rate of the steel plate was 15° C./S, and the final temperature was 480° C.
  • Example 1 It was performed as Example 1 with the exception that the heating was performed at 1120° C. for 180 mins, wherein the start rolling temperature in the first stage of rolling was 1050° C., and the thickness of the rolled piece was 120 mm; the start rolling temperature in the second stage of rolling was 820° C., the Pass deformation rate was 15-25%, the finish rolling temperature was 780° C., and the thickness of the finished steel plate was 40 mm; and, the cooling rate of the steel plate was 20° C./S, and the final temperature was 540° C.
  • % % 1 0.04 0.35 1.80 0.070 0.055 0.02 0.015 0.30 0.0018 balance 0.176 2 0.03 0.60 1.50 0.045 0.45 0.03 0.02 0.22 0.001 balance 0.189 3 0.04 0.40 2.2 0.035 0.10 0.04 0.012 0.10 0.0011 balance 0.186 4 0.05 0.55 1.50 0.040 0.15 0.03 0.01 0.25 0.0015 balance 0.183 5 0.06 0.05 1.45 0.065 0.30 0.03 0.02 0.20 0.0010 balance 0.183 6 0.06 0.15 1.30 0.047 0.03 0.02 0.03 0.25 0.0020 balance 0.180
  • Example 1 of the present invention The steel plate with a low welding crack susceptibility of Example 1 of the present invention was tested for its weldability (small Tekken test). Under ambient temperature and 50° C., no crack was observed (See Table 3), indicating that the steel plate of the present invention had excellent welding property and typically no preheating was needed when welding.
  • Example 5 of the present invention was studied for its microscopic structure, and its scanning electron microscope (SEM) micrograph and transmission electron microscope (TEM) micrograph are shown in FIG. 1 a and FIG. 1 b , respectively.
  • SEM scanning electron microscope
  • TEM transmission electron microscope
  • the bainite batten was thinned, and carbide precipitated out on the edge of the bainite batten, and fine carbide also precipitated out on the bainite batten. From FIG. 1 b , it could be seen that the bainite batten was comprised of fine nano-scale bainite batten.
  • the steel plate of the present invention has fine banite batten structure and ultrafine nano-scale banite batten sub-structure.
  • the ultrafine banite batten structure provides fine grain strengthening effect
  • the second phase particles precipitating out along the grain boundary of the ultrafine banite batten provide precipitation strengthening effect
  • the dislocation structure within the ultrafine banite batten provides dislocation strengthening effect, and, the combined action of these strengthening effects guarantees the strength and toughness of the steel plate of the present invention.
  • the chemical components are reasonably designed by greatly reducing the content of C, partly replacing Mo with cheap alloy elements such as Mn, replacing the precipitation strengthening effect of Cu with the precipitation strengthening effect of fine precipitated particles of carbonitride of V, and adding no noble elements such as Ni.
  • the content of the alloy element is low, the cost of the starting materials is low, the welding crack susceptibility is low and no preheating is needed before welding.
  • the steel plate of the present invention does not need any additional thermal refining treatment, the manufacturing procedure is simplified and the manufacture cost of the steel is reduced.
  • the yield strength of the steel plate with a low welding crack susceptibility of the present invention is larger than 800 MPa, the tensile strength is larger than 900 MPa, and the Charpy impact energy Akv ( ⁇ 20° C.) is ⁇ 150 J; and, the thickness of the plate is up to 60 mm, the welding crack susceptibility index Pcm is ⁇ 0.20%, and the steel plate has excellent low-temperature toughness and weldability.

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US12/524,311 2007-10-26 2008-10-24 Steel plate having a low welding crack susceptibility and a yield strength of 800MPa and manufacture method thereof Active 2029-10-20 US8702876B2 (en)

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CN200710094177.2 2007-10-26
CN200710094177 2007-10-26
PCT/CN2008/072807 WO2009056055A1 (fr) 2007-10-26 2008-10-24 Tôle d'acier à limite d'élasticité de grade 800 mpa et faible sensibilité à la fissuration de soudure, et son procédé de fabrication

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RU2458754C1 (ru) * 2011-03-17 2012-08-20 Открытое акционерное общество "Магнитогорский металлургический комбинат" Способ производства листов из низколегированной трубной стали класса прочности х70
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DE112008000562T5 (de) 2010-01-28
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CN101418416B (zh) 2010-12-01
KR20100070310A (ko) 2010-06-25
US20100032062A1 (en) 2010-02-11
FI20095872A (fi) 2009-08-25
KR101563929B1 (ko) 2015-10-28
EP2218801A4 (en) 2012-02-01
EP2218801A1 (en) 2010-08-18
SE0900863L (sv) 2009-07-27
WO2009056055A1 (fr) 2009-05-07
ZA200901450B (en) 2010-08-25
DE112008000562B4 (de) 2013-05-29
SE535302C2 (sv) 2012-06-19
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EP2218801B1 (en) 2013-05-01
ES2424009T3 (es) 2013-09-26

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